1. Field of the Invention
The present invention relates to the field of thermoplastic polymeric compositions, and specifically to filled blends of the copolymers of ethylene and vinyl acetate.
2. Description of the Related Art
One or more patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
The practical applications of ethylene vinyl acetate (EVA) copolymers are diverse. For example, EVA copolymers are used in flexible shrink wrap, footwear soles, hot melt and heat seal adhesives, flexible toys, tubing, wire coatings, medical gloves, masks, automotive carpet, foam, fabric or scrim material, sound-dampening and the like.
Two parameters of EVA copolymers that affect their intended utility are the level of vinyl acetate comonomer and the melt index. At low comonomer levels, the EVA copolymer has a high degree of polyethylene crystallinity. As the percent of vinyl acetate increases, the vinyl acetate disrupts the polyethylene crystallinity and, accordingly, melting and freezing points decrease. A copolymer having a high melt index, which is correlated with a low molecular weight, is expected to be softer and have a lower melting temperature, for example. As the melt index decreases, the copolymer's properties also change, as expected for higher molecular weight polymers.
EVA copolymers have been blended with other polymers. For example, Cser et al. ((2002) J. Therm. Anal. Calorim. 70:651-662) describes the miscibility of a cross-linked ethylene vinyl acetate copolymer and linear low density polyethylene (LLDPE) blended with virgin LLDPE.
In addition, Wang et al. ((2002) J. Appl. Polymer Sci. 85:2485-2490) discloses that while EVA copolymer improves the processing and ductile properties of LLDPE highly loaded with aluminum hydroxide, there was a concomitant deterioration of the tensile strength.
U.S. Pat. No. 6,723,793 describes a foam blend comprising A) a heterogenous or homogeneous linear ethylene homopolymer or interpolymer; and B) a branched homopolymer or interpolymer.
U.S. patent application Ser. No. 10/003,639 describes a rotational molding composition comprising A) a majority component of one or more homopolymers or interpolymers such as a LLDPE, wherein the homopolymer or interpolymer is 70 percent or greater by weight of the composition; and B) one or more impact additives such as an ethylene-vinyl acetate copolymers (EVA) having a vinyl acetate content of about 2 to about 50 weight percent, wherein the impact additive is about 2 to about 50 percent of the molding composition; and wherein the impact strength of the composition at a fixed temperature is increased by at least 0.1 ft-lb/in from that of the majority component in the absence of the impact additive. The composition can also contain less than about 10 weight percent of filler.